Precision flow gear pump

ABSTRACT

A positive displacement gear pump including a pump housing having an inlet port, an outlet portion, and first and second pumping chambers. A first gear having helical teeth is engaged with an inner surface of the first pumping chamber. A second gear with helical teeth is engaged with an inner surface of the second pumping chamber. At least two teeth on the first and second gears are simultaneously meshed in a meshed region. A first bearing element is located at one end surface of the first and second gears. The first bearing insert includes at least a first outlet channel fluidly coupling an outlet portion of the meshed region to the outlet port.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional application Ser. No. 60/825,049, entitled PRECISION FLOW GEAR PUMP, filed Sep. 8, 2006, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a precision flow gear pump, and in particular, to a gear pump that vents fluid trapped between the helical gear teeth in a manner that minimizes pulsations and dramatically reduces variation in flow rate.

BACKGROUND OF THE INVENTION

Gear pumps used for pumping fluid utilize a drive gear and a driven gear that mesh proximate inlet and discharge openings of the pump. The drive gear rotates the driven gear. For each tooth there is a line contact between the leading flank of the drive gear and trailing flank of the driven gear. As the drive gear and driven gear rotate fluid fills the gap between adjacent teeth and is carried from the inlet through an adjacent transition zone to the outlet. When there is sealing action in the mesh of the teeth and displacement of fluid by a mating tooth, the pump is classified as a “positive displacement gear pump.”

The pumps of this type for high pressures are generally produced with a so-called “balanced” or “equilibrated” configuration, in which the two opposing faces of the bushings for supporting the gears are subjected to pressures over areas that generate a moderate differential force which tends to keep each bushing in contact with the gears. The pressure on the bushings tend to minimize the leakages over the faces of the gears themselves as a result of the difference in pressure between the inlet and outlet.

Obtaining good leak-tightness between the inlet and outlet side of the gears is important to the efficiency of gear pumps. Another problem which the manufacturers of pumps have to deal with is the noise of the pumps due to the phenomena of cavitations in the transfer of the fluid. A study of the above-mentioned problems linked to the design of gear pumps is set out in “C. Bonacini, Sulla portata delle pompe ad ingranaggi (On the efficiency of gear pumps), L'ingegnere, 1961 n. 9”. Oscillations generate a pulsating wave that is transmitted to the surroundings and in particular to the walls of the pump. The noise produced can reach levels which are also unpredictable where the above-mentioned members begin to resonate with the frequency of oscillation or ripple. As the speed of the pump increases and/or as discharge pressure increases, pump damage occurs more quickly and cavitations is more intense. Cavitations can damage gear pumps and result in non-uniform flow of the fluid.

Various embodiments of gear pumps are illustrated in U.S. Pat. Nos. 4,548,562 (Hughson); 6,123,533 (McBurnett et al.); and 6,887,055 (Morselli), the disclosures of which are hereby incorporated by reference.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a precision flow, positive displacement gear pump that vents fluid trapped between the helical gear teeth in a manner that minimizes pulsations. The present gear pump also permits different gears and bearing elements to be substituted to change pump flow characteristics.

In the illustrated embodiment, the pump includes a pump housing having an inlet port, an outlet port, and first and second pumping chambers. A first gear having helical teeth is engaged with an inner surface of the first pumping chamber. A second gear with helical teeth is engaged with an inner surface of the second pumping chamber. At least two teeth on the first and second gears are simultaneously meshed in a meshed region. A first bearing element is located on the end surfaces of the first and second gears. The first bearing insert includes a first outlet channel fluidly coupling an outlet portion of the meshed region to the outlet port.

The meshed region preferably has at least two line contacts between the first and second gears that form a fluid-tight barrier between the inlet port and the outlet port.

In another embodiment, the first bearing element includes a first inlet channel fluidly coupling an inlet portion of the meshed region with the inlet port. A first land region separates the first outlet channel from the first inlet channel. The first land region preferably prevents fluid communication between the inlet port and the outlet port. The location of the first land region is typically a function of an angle of the helical teeth. In one embodiment, the first land region has a length separating the inlet channels from the outlet channels on the first bearing insert that is greater than or equal to a width of the teeth at a pitch circle. In another embodiment, a width of the inlet and outlet channels on the first bearing insert is greater than or equal to twice the addendum of the teeth.

In another embodiment, a second bearing insert is provided at the other ends of the gears. The second bearing insert includes a second outlet channel fluidly coupling the outlet portion of the meshed region with the outlet port and a second inlet channel fluidly coupling the inlet portion of the meshed region with the inlet port. A second land region separates the second outlet channel from the second inlet channel.

The first and second gears and the first bearing inserts are preferably removable from the pump housing. The modular nature of the present gear pump means that the first and second gears can be replaced with third and fourth gears having an axial length different from an axial length of the first and second gears. One or more bearing inserts are combined with the third and fourth gears so that the overall axial length is the same as the axial length of the first and second gears and the first and second bearing insert.

In another embodiment, the third and fourth gears have a tooth helix angle different from a tooth helix angle on the first and second gears.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of a precision flow gear pump in accordance with an embodiment of the present invention.

FIG. 2 illustrates an inner surface of a rear cover on the gear pump of FIG. 1.

FIG. 3A illustrates an inner surface of a front cover on the gear pump of FIG. 1.

FIG. 3B is a sectional view of the front cover of FIG. 3A.

FIG. 3C illustrates an outer surface of the front cover of FIG. 3A.

FIG. 4 is a sectional view of the gear pump of FIG. 1.

FIG. 5 is a schematic illustration of a meshed region in accordance with an embodiment of the present invention.

FIG. 6A illustrates an inner surface of a bearing insert in accordance with an embodiment of the present invention.

FIG. 6B is a sectional view of the bearing insert of FIG. 6A.

FIG. 6C illustrates an outer surface of the bearing insert of FIG. 6A.

FIG. 7A illustrates an inner surface of a bearing insert in accordance with an embodiment of the present invention.

FIG. 7B is a sectional view of the bearing insert of FIG. 7A.

FIG. 7C illustrates an outer surface of the bearing insert of FIG. 7A.

FIG. 8 is a side view of a gear and bearing insert assembly in accordance with an embodiment of the present invention.

FIG. 9 is a side view of an alternate gear and bearing insert assembly in accordance with an embodiment of the present invention.

FIG. 10A illustrates an outer surface of a bearing insert in accordance with an embodiment of the present invention.

FIG. 10B is a sectional view of the bearing insert of FIG. 10A.

FIG. 10C illustrates an inner surface of the bearing insert of FIG. 10A.

FIG. 11A illustrates an outer surface of a bearing insert in accordance with an embodiment of the present invention.

FIG. 11B is a sectional view of the bearing insert of FIG. 11A.

FIG. 11C illustrates an inner surface of the bearing insert of FIG. 11A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross-sectional view of a precision flow gear pump 20 in accordance with an embodiment of the present invention. Pump assembly 22 includes cylinder housing 24 enclosed by rear cover 26 and front cover 28. The front cover 28 optionally includes one or more seals 32 that extend around drive shaft 34. Thrust washer 30 is provided to axially retain the drive shaft 34 to the pump assembly 22.

Helical drive gear 38 coupled to drive shaft 34 is located in pump chamber 60. Helical driven gear 40 mounted on driven shaft 42 is located in pump chamber 70. The drive gear 38 is meshed with driven gear 40 in meshed region 80. Helical gears have a cylindrical shape wherein the teeth are set at an angle to the axis.

First bearing insert 50 is positioned between first ends 53 of the gears 38, 40 and inside surface 52 of the rear cover 26. Second bearing insert 54 is located between second ends 56 of the gears 38, 40 and inside surface 58 of the front cover 28.

FIG. 2 illustrates inside surface 52 of the rear cover 26. In the illustrated embodiment, inside surface 52 includes seal recess 46A and driven shaft thrust disc recess 48A. The seal recess 46A receives a seal that engages with rear surface 131 of the cylinder 24 (see FIG. 1).

FIG. 3A illustrates the inside surface 58 of the front cover 28. The front cover 28 includes drive shaft hole 78 sized to receive the drive shaft 34. FIG. 3B is a side sectional view of the front cover 28. FIG. 3C illustrates outer surface 68 of the front cover 28. The inside surface 58 includes a seal recess 46B and driven shaft thrust disc recess 48B. The driven shaft thrust disc recess 48A is aligned with the driven shaft thrust disc recess 48B. In the illustrated embodiment, the seal recess 46A is aligned with the seal recess 46B. The seal recess 46B receives a seal that engages with rear surface 157 of the cylinder 24 (see FIG. 1).

FIG. 4 is a cross-sectional view of the precision flow gear pump 20 of FIG. 1. Teeth 62 on the drive gear 38 engage with perimeter surface 64 of the pump chamber 60. Teeth 72 engage with perimeter surface 74 of the pump chamber 70. In the illustrated embodiment, drive gear 38 and driven gear 40 are preferably attached to the shafts 34, 42 by keys 66, 76, respectively, to facilitate easy replacement and simultaneous rotational operation.

In the preferred embodiment, the engagement of the teeth 62, 72 with the respective perimeter surfaces 64, 74 is sufficient to block the free flow of fluid between the inlet cavity 92 and outlet cavity 100. Consequently, fluid preferably moves from the inlet cavity 92 to the outlet cavity 100 only when the pump 20 is in the operation mode. Helical gears 38, 40 bring more teeth into mesh in meshed region 80 than a spur gear, so helical gears are quieter and smoother at high speeds.

In the operation mode, drive shaft 34 rotates the drive gear 38 in the direction 82. The teeth 62 on the drive gear 38 are meshed with the teeth 72 on the driven gear 40 in meshed region 80 to rotate the driven gear 40 in the direction 84. A portion of the fluid entering inlet port 89 advances to inlet cavity 92 and is captured in tooth space 90 between the drive gear 38 and the perimeter surface 64 of the pump chamber 60. Simultaneously, fluid is trapped in tooth space 91 on driven gear 40 and advanced around the perimeter surface 74 to the outlet cavity 100 in the direction 84.

As the gear 38, 40 rotate in the directions 82, 84 the fluid is advanced around the pump chambers 60, 70 to the outlet cavity 100. As fluid pressure in the outlet cavity 100 increases the fluid is advanced through the outlet port 102. In the operation mode, the fluid pressure in the outlet cavity 100 is greater than in the inlet cavity 92.

During operation of the pump 20, some portion of the fluid in the outlet cavity 100 is captured by tooth spaces 90A, 91A and is drawn into the outlet portion 80B of the meshed region 80. After the fluid is substantially expelled from the outlet portion 80B of the meshed region, the teeth 62, 72 start to separate creating expanding chambers, such as for example the chamber 106AB in FIG. 5.

As best illustrated in FIG. 5, at least two teeth 62, 72 of the gears 38, 40 mesh in the meshed region 80. The meshed teeth 62, 72 form a number of line contacts 104A, 104B, 104C, 104D (referred to collectively as “104”) in the meshed region 80. The contact lines 104 are preferably sufficient to prevent fluid communication between the inlet cavity 92 and the outlet cavity 100. As used herein, “meshed region” refers to a cross-sectional area of engagement between a drive gear and a driven gear bounded by an outermost line contact between teeth on an inlet side and an outermost line contact on an outlet side. In the embodiment of FIG. 5, the outermost line contacts are 104A and 104D. The meshed region times the length of the gears 38, 40 is a meshed volume.

Adjacent line contacts 104 are the boundaries for chambers 106AB, 106BC, 106CD (referred to collectively as “106”). As the teeth 62, 72 advance some of the fluid is expelled in direction 116 to the outlet cavity 100. Some portion of the fluid in the outlet portion 80B of the meshed region 80, however, is compressed between the gears 38, 40. As used herein, “outlet portion of a meshed region” refers to a cross-sectional area of engagement between a drive gear and a driven gear bounded by an outermost line contact on an inlet side where fluid is compressed between teeth in the meshed region and an outermost line contact on an outlet side. In embodiment of FIG. 5, the outlet portion 80B of the meshed region 80 includes chambers 106BC and 106CD. The outlet region 80B of the meshed area 80 is bounded by the outermost line contact 104B on an inlet side 92 and an outermost line contact 104D on the outlet cavity 100.

Unless an exit path is provided from the chambers 106BC and 106CD in the outlet portion 80B the trapped fluid 110, which is typically substantially incompressible, will cause pump vibration and noise. Over time, trapped fluid will damage the pump 20. The trapped fluid also causes flow rate variation that is undesirable for some applications.

In the preferred embodiment, fluid trapped in the chambers 106 is expelled axially along the length of the teeth 62, 72 to the first and second ends 53, 56 of the gears 38, 40 and the bearing inserts 50, 54 (see FIG. 1). As illustrated in FIGS. 6A and 7A, the fluid passes through channels 128 and 150 in the bearing inserts 50, 54, respectively, to the outlet cavity 100.

After the fluid is expelled from the chambers 106BC and 106CD, the teeth 62, 72 advance to the inlet region 80A of the meshed region 80 and start to separate creating expanding chamber 106AB. Once the teeth 62, 72 separate a sufficient amount to break line contact 104A, fluid will rush into the empty chamber 106AB, causing vibration and cavitations. To avoid this problem, fluid is preferably directed from the inlet cavity 92 to the chamber 106AB through the channels 126, 152 in the bearing inserts 50, 54 (See FIGS. 6A and 7A) before the line contact 104A separates. As used herein, “inlet portion of a meshed region” refers to a cross-sectional area of engagement between a drive gear and a driven gear bounded by an outermost line contact on an inlet side and an outermost line contact on an outlet side where fluid is drawn into spaces between teeth in the meshed region. In the embodiment of FIG. 5, the inlet portion 80A of the meshed region 80 includes chamber 106AB. The inlet region 80A of the meshed area 80 is bounded by the outermost line contact 104A on an inlet side 92 and an outermost line contact 104B on the outlet cavity 100.

FIGS. 6A through 7C illustrate various views of the first and second bearing inserts 50, 54 illustrated in FIG. 1. Perimeter edges 120 have a shape corresponding to perimeter surfaces 64, 74 of the pump chambers 60, 70 (see FIG. 4). Drive shaft holes 122 are sized to receive the drive shaft 34 and driven shaft holes 124 are sized to receive the driven shaft 42.

Front surface 146 of the first bearing insert 50 includes channel 126 sized and positioned to be in fluid communication with inlet cavity 92 and the inlet portion 80A of the meshed region 80. Channel 128 is sized and positioned to be in fluid communication with the outlet cavity 100 and the outlet portion 80B of the meshed region 80. Land 142 separates the channel 126 from the channel 128.

Front surface 151 of the second bearing insert 54 includes channel 152 sized and positioned to be in fluid communication with inlet cavity 92 and the inlet portion 80A of the meshed region 80. Channel 150 is sized and positioned to be in fluid communication with the outlet cavity 100 and the outlet portion 80B of the meshed region 80. Land 154 separates the channel 150 from the channel 152.

Channels 126, 128, 150, 152 preferably have a width 140 that is at least twice as wide as the addendum of the teeth 62, 72. Lands 142, 154 are positioned to prevent the outlet cavity 100 from fluidly communicating with the inlet cavity 92. Width 144 of the lands 142, 154 is sized to be greater than or equal to the width of an individual tooth 62, 72 at the pitch circle. Pitch Circle is a theoretical circle that rolls without slipping with the pitch circle of the mating gear. The location of the lands 142, 154 is determined by the pitch of the teeth 62, 72 and the helical angle of the teeth relative to a longitudinal axes 182 (see FIGS. 8 and 9) of the gears 38, 40.

Rear surfaces 130, 155 of the bearing inserts 50, 54 preferably include various channels 132, 153 fluidly coupled to inlet cavity 92. Pressure in the outlet cavity 100 is greater than in the inlet cavity 92 during operation of the pump 20. Consequently, fluid may migrate between the rear surfaces 130, 155 of the bearing elements 50, 54 and the respective inside surfaces 52, 58 of the covers 26, 28. Any higher pressure fluid in the channels 132, 153 is vented to the inlet cavity 92.

In an alternate embodiment, the bearing insert 50 includes the channels 126, 128, but the front surfaces 151 of the second bearing insert 54 is substantially flat without any of the channels 150, 152. In this embodiment fluid would be expelled and drawn into the respective portions 80B, 80A of the meshed region 80 only along the ends 53 of the gears 38, 40.

In another embodiment, the bearing insert 50 includes the outlet channels 128, but not the inlet channels 126 and the bearing insert 54 includes the inlet channels 150 but not the outlet channels 152. In this embodiment, fluid is expelled along the ends 53 of the gears 38, 40 and is drawn into the input region 80A of the meshed region 80 along the ends 56.

The bearing inserts 50, 54 can be made from a variety of materials, such as metal, plastics, ceramics, and the like. In the illustrated embodiment, the bearing inserts 50, 54 are constructed from glass-filled Teflon.

As best illustrated in FIG. 8, fluid trapped located between the teeth 62, 72 in the outlet portion 80B of the meshed region 80 is expelled along the axial length of the gear teeth 62, 72 and out through the channels 128, 150 to the outlet cavity 100 as indicated by arrows 125. Fluid located in the inlet cavity 92 is drawn through the channels 126, 152 to the inlet portion 80A of the meshed region 80 (and into the chamber 106AB in FIG. 5) as indicated by arrows 127.

FIG. 8 is a side view of a gear assembly 158 suitable for use in the precision flow gear pump 20 of FIG. 1. The gears 38, 40 and the first and second bearing inserts 50, 54 are sized so that the total axial length 160 of the gear assembly 158 corresponds to the distance between the inner surface 52 of the rear cover 26 and the inside surface 58 of the front cover 28. The land regions 142, 154 of the first and second bearing inserts 50, 54 are positioned so that fluid trapped between contact lines of meshed teeth (see FIG. 5) is driven axially along the paths 125 to the channels 152, 150.

The positions of the lands 142, 154 correspond to the angle 180 of the teeth 62, 72 relative to longitudinal axes 182 of the gears 38, 40. The gears 38, 40 have a length 176 and a helix angle 180 that permits at least two teeth to engage with the driven gear (see FIG. 4). As the length 176 of the gears 38, 40 is changed, the helix angle 180 also needs to change to maintain engagement of at least two teeth in the meshed region 80. The location of the lands 142, 154 also needs to be shifted to correspond to the helix angle 180.

FIG. 9 is a side view of an alternate gear assembly 198 with a gear 200 having a different axial length 202 and a different helix angle 204 than the gears 38, 40. First and second bearing inserts 210, 212 are selected to have thicknesses 214, 216 so that the overall axial length 218 is substantially the same as the axial length 160 of the gear assembly of FIG. 8. Land areas 220 on the first and second bearing inserts 210, 212 have a width corresponding to the pitch of the gear teeth 206. The position of the lands 220 corresponds to the helix angle 204 of the gear teeth 206.

The gear assemblies 158, 198 are merely exemplary embodiments. A variety of different gear assemblies can be used with a single gear pump in accordance with the present invention. For example, by varying the height of the gears and the bearing inserts, the tooth pitch, and the helix angle, different pumping characteristics can be achieved using the gear pump in accordance with the present invention. Consequently, the present gear pump can preferably be modified for different applications simply by replacing the gear assemblies.

Table 1 contains a summary of performance data for a model 4400-10 gear pump available from McNally Industries, Inc. located in Gransburg, Wis. and Example A, a gear pump made according to the embodiment of FIGS. 6A-7C. The average flow rate in gallons per minute (GPM) is similar between the 4400-10 and Example A for constant revolutions per minute (RPM), viscosity in centipoises (cP), and average pressure in pounds per square inch (PSI). The gear pump of Example A, however, provides an 83.5% reduction in flow rate variation. It is contemplated that the flow of fluid through the channels in the bearing inserts 50, 54 reduces vibration, pump wear and flow rate variation.

TABLE 1 Gear Flow Rate Configuration Ave. Ave Flow Flow Rate Variation, % Flow Rate # of Viscosity Pressure Rate Variation of Ave Flow Variation Pump Type Teeth RPM (cP) (PSI) (GPM) (GPM) Rate Reduction 4400-10 Helical 12 150 80 25 0.48760 0.032816 6.73% Ex. A Helical 26 150 80 25 0.44900 0.003555 0.79% 88.24% 4400-10 Helical 12 150 80 50 0.48200 0.045796 9.50% Ex. A Helical 26 150 80 50 0.44250 0.008759 1.98% 79.17% 4400-10 Helical 12 150 800 25 0.49300 0.009759 1.98% Ex. A Helical 26 150 800 25 0.43850 0.001736 0.40% 80.00% 4400-10 Helical 12 150 800 50 0.49230 0.017540 3.56% Ex. A Helical 26 150 800 50 0.42150 0.002002 0.48% 86.67%

FIGS. 10A-11C illustrate various views of alternate first and second bearing inserts 250, 254 illustrated in FIG. 1. Drive shaft holes 122 are sized to receive the drive shaft 34 and driven shaft holes 124 are sized to receive the driven shaft 42. Perimeter edges 252 have a shape corresponding to perimeter surface 256 of the four-lobed cavity 258 in the cylinder housing 24. Lobes 260, 262 on the first bearing insert 250 extending in the inlet cavity 92 and outlet cavity 100, respectively along the rear of the gear pump 20. Lobes 264, 266 on the second bearing insert 254 extending into the inlet cavity 92 and outlet cavity 100, respectively, along the front of the gear pump 20. The lobes, 260, 262, 264, 266 reduce the amount of idle fluid within the gear pump 20.

Front surface 270 of the first bearing insert 250 includes channel 272 sized and positioned to be in fluid communication with outlet cavity 100 and the outlet portion 80B of the meshed region 80. During operation of the pump 20, a portion of the fluid in the outlet portion 80B of the meshed region 80 is expelled axially along the gears 38, 40, through the channel 272 in the first bearing insert 250, and out to the outlet cavity 100. The channel 272 preferably has a width 140 that is at least twice as wide as the addendum of the teeth 62, 72. In the illustrated embodiment, front surface 280 of the second bearing insert 254 does not include any channels.

Rear surfaces 282, 284 of the bearing inserts 250, 254 preferably include various channels 286, 288 fluidly coupled to inlet cavity 92 though ports 290, 292, respectively. Pressure in the outlet cavity 100 is greater than in the inlet cavity 92 during operation of the pump 20. Consequently, fluid may migrate between the rear surfaces 282, 284 of the bearing elements 250, 254 and the respective inside surfaces 52, 58 of the covers 26, 28. Any higher pressure fluid in the channels 286, 288 is vented to the inlet cavity 92.

Table 2 contains a summary of performance data for a model No. 31FS1633L00V00 spur gear pump available from Liquiflo, located in Garwood, N.J. (www.liquiflo.com) and Example B, a gear pump made according to the embodiment of FIGS. 10A-11C. The average flow rate in gallons per minute (GPM) is similar between the Liquiflo Pump and Example B for constant revolutions per minute (RPM), viscosity in centipoises (cP), and average pressure in pounds per square inch (PSI). The gear pump of Example B, however, provides an average of 77.4% reduction in flow rate variation.

TABLE 2 Flow Rate Ave. Ave Flow Flow Rate Variation, Flow Rate Gear Viscosity Pressure Rate Variation % of Ave Variation Pump Configuration RPM (cP) (PSI) (GPM) (GPM) Flow Rate Reduction Liquiflo Spur 12 50 1000 1 0.013 5.14648E−05 0.40% Ex. B Helical 26 50 1000 1 0.014 6.92795E−06 0.05% 87.50% Liquiflo Spur 12 50 1000 25 0.011 1.82898E−05 0.17% Ex. B Helical 26 50 1000 25 0.013 3.85986E−06 0.03% 82.14% Liquiflo Spur 12 50 1000 50 0.012 2.61283E−05 0.22% Ex. B Helical 26 50 1000 50 0.013 7.71971E−06 0.06% 72.73% Liquiflo Spur 12 50 1000 75 0.016  1.6891E−05 0.11% Ex. B Helical 26 50 1000 75 0.012 6.33413E−06 0.05% 50.00% Liquiflo Spur 12 50 1000 100 0.012 3.32542E−05 0.28% Ex. B Helical 26 50 1000 100 0.011 8.70942E−06 0.08% 71.43% Liquiflo Spur 12 100 1000 1 0.027 0.000106888 0.40% Ex. B Helical 26 100 1000 1 0.029 1.43508E−05 0.05% 87.50% Liquiflo Spur 12 100 1000 25 0.023 3.46002E−05 0.15% Ex. B Helical 26 100 1000 25 0.025 9.89707E−06 0.04% 73.68% Liquiflo Spur 12 100 1000 50 0.029  5.7403E−05 0.20% Ex. B Helical 26 100 1000 50 0.024 1.42518E−05 0.06% 70.00% Liquiflo Spur 12 100 1000 75 0.025 7.25785E−05 0.29% Ex. B Helical 26 100 1000 75 0.024 1.26683E−05 0.05% 81.82% Liquiflo Spur 12 100 1000 100 0.025 6.92795E−05 0.28% Ex. B Helical 26 100 1000 100 0.025 9.89707E−06 0.04% 85.71% Liquiflo Spur 12 150 1000 1 0.042 0.000249406 0.59% Ex. B Helical 26 150 1000 1 0.04 3.95883E−05 0.10% 83.33% Liquiflo Spur 12 150 1000 25 0.037 5.85907E−05 0.16% Ex. B Helical 26 150 1000 25 0.039 1.92993E−05 0.05% 68.75% Liquiflo Spur 12 150 1000 50 0.039 6.17577E−05 0.16% Ex. B Helical 26 150 1000 50 0.037 1.46477E−05 0.04% 75.00% Liquiflo Spur 12 150 1000 75 0.038 0.000110319 0.29% Ex. B Helical 26 150 1000 75 0.038 2.00581E−05 0.05% 81.82% Liquiflo Spur 12 150 1000 100 0.037 0.000109857 0.30% Ex. B Helical 26 150 1000 100 0.041 2.43468E−05 0.06% 80.00% Liquiflo Spur 12 200 1000 1 0.057 0.000451306 0.79% Ex. B Helical 26 200 1000 1 0.054 2.67221E−05 0.05% 93.75% Liquiflo Spur 12 200 1000 25 0.047 6.32621E−05 0.13% Ex. B Helical 26 200 1000 25 0.052 2.05859E−05 0.04% 70.59% Liquiflo Spur 12 200 1000 50 0.052 0.00010293  0.20% Ex. B Helical 26 200 1000 50 0.05 1.97941E−05 0.04% 80.00% Liquiflo Spur 12 200 1000 75 0.052 0.000123515 0.24% Ex. B Helical 26 200 1000 75 0.047 2.48087E−05 0.05% 77.78% Liquiflo Spur 12 200 1000 100 0.052 0.000144101 0.28% Ex. B Helical 26 200 1000 100 0.049 3.87965E−05 0.08% 71.43% Liquiflo Spur 12 250 1000 1 0.063 0.000685867 1.09% Ex. B Helical 26 250 1000 1 0.074 7.32383E−05 0.10% 90.91% Liquiflo Spur 12 250 1000 25 0.065 7.71971E−05 0.12% Ex. B Helical 26 250 1000 25 0.066 2.61283E−05 0.04% 66.67% Liquiflo Spur 12 250 1000 50 0.066 0.000117577 0.18% Ex. B Helical 26 250 1000 50 0.063 2.49406E−05 0.04% 77.78% Liquiflo Spur 12 250 1000 75 0.065 0.000137239 0.21% Ex. B Helical 26 250 1000 75 0.069 3.64212E−05 0.05% 75.00% Liquiflo Spur 12 250 1000 100 0.068 0.0002019  0.30% Ex. B Helical 26 250 1000 100 0.063 3.74109E−05 0.06% 80.00%

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. 

1. A positive displacement gear pump comprising: a pump housing having an inlet port, an outlet port, and first and second pumping chambers; a first gear having helical teeth engaged with an inner surface of the first pumping chamber and a second gear with helical teeth engaged with an inner surface of the second pumping chamber, at least two teeth on the first and second gears simultaneously meshed in a meshed region; and a first bearing insert located at a first end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the first bearing insert including a first outlet channel fluidly coupling an outlet portion of the meshed region with the outlet port.
 2. The positive displacement gear pump of claim 1 wherein the first bearing insert comprises a first inlet channel fluidly coupling an inlet portion of the meshed region with the inlet port, and a first land region separating the first outlet channel from the first inlet channel.
 3. The positive displacement gear pump of claim 2 wherein the first land region prevents fluid communication between the inlet port and the outlet port.
 4. The positive displacement gear pump of claim 2 wherein the location of the first land region is a function of an angle of the helical teeth.
 5. The positive displacement gear pump of claim 2 wherein the first land region has a length separating the inlet channels from the outlet channels on the first bearing insert that is greater than or equal to a width of the teeth at a pitch circle.
 6. The positive displacement gear pump of claim 2 wherein a width of the inlet channels and the outlet channels on the first bearing insert is greater than or equal to twice the addendum of the teeth.
 7. The positive displacement gear pump of claim 1 comprising a second bearing insert located at a second end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the second bearing insert including a second outlet channel fluidly coupling the outlet portion of the meshed region with the outlet port, a second inlet channel fluidly coupling the inlet portion of the meshed region with the inlet port, and a second land region separating the second outlet channel from the second inlet channel.
 8. The positive displacement gear pump of claim 1 comprising a second bearing insert located at a second end of the first and second pumping chambers and engaged with end surfaces of the first and second gears.
 9. The positive displacement gear pump of claim 8 comprising: third and fourth gears having an axial length different from an axial length of the first and second gears; and third and fourth bearing insert having a thickness different than a thickness of the first and second bearing insert, so an axial length of the third and fourth gear and the third and fourth bearing insert is the same as an axial length of the first and second gears and the first and second bearing insert.
 10. The positive displacement gear pump of claim 9 wherein a third outlet channel on the third bearing insert comprises a length different than a length of the first outlet channel on the first bearing insert.
 11. The positive displacement gear pump of claim 8 comprising: third and fourth gears with a tooth helix angle different from a tooth helix angle on the first and second gears; and third and fourth bearing inserts having a thickness different than the first and second bearing inserts, so an axial length of the third and fourth gear and the third and fourth bearing inserts is the same as an axial length of the first and second gears and the first and second bearing inserts.
 12. The positive displacement gear pump of claim 1 wherein the first and second gears and the first bearing inserts are removable from the pump housing.
 13. The positive displacement gear pump of claim 1 wherein the meshed region comprises at least two line contacts between the first and second gears that form a fluid-tight barrier between the inlet port and the outlet port.
 14. A positive displacement gear pump comprising: a pump housing having an inlet port, an outlet port, and first and second pumping chambers; a first gear having helical teeth engaged with an inner surface of the first pumping chamber and a second gear with helical teeth engaged with an inner surface of the second pumping chamber, the first and second gears comprising teeth at a helical angle so that at least two teeth are simultaneously meshed in a meshed region; and a first bearing insert located at a first end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the first bearing insert including a first outlet channel fluidly coupling an outlet portion of the meshed region with the outlet port, a first inlet channel fluidly coupling an inlet portion of the meshed region with the inlet port, and a first land region separating the first outlet channel from the first inlet channel.
 15. A positive displacement gear pump comprising: a pump housing having an inlet port, an outlet port, and first and second pumping chambers; a first gear having helical teeth engaged with an inner surface of the first pumping chamber and a second gear with helical teeth engaged with an inner surface of the second pumping chamber, at least two teeth on the first and second gears simultaneously meshed in a meshed region; a first bearing insert located at a first end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the first bearing insert including a first outlet channel fluidly coupling an outlet portion of the meshed region with the outlet port, a first inlet channel fluidly coupling an inlet portion of the meshed region with the inlet port, and a first land region separating the first outlet channel from the first inlet channel; and a second bearing insert located at a second end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the second bearing insert including a second outlet channel fluidly coupling the outlet portion of the meshed region with the outlet port, a second inlet channel fluidly coupling the inlet portion of the meshed region with the inlet port, and a second land region separating the second outlet channel from the second inlet channel.
 16. The positive displacement gear pump of claim 15 comprising: third and fourth gear having an axial length different from an axial length of the first and second gears; and third and fourth bearing inserts having a thickness different than a thickness of the first and second bearing inserts, so an axial length of the third and fourth gear and the third and fourth bearing inserts is the same as an axial length of the first and second gears and the first and second bearing inserts.
 17. A positive displacement gear pump comprising: a pump housing having an inlet port, an outlet port, and first and second pumping chambers; a first gear having helical teeth engaged with an inner surface of the first pumping chamber and a second gear with helical teeth engaged with an inner surface of the second pumping chamber, at least two teeth on the first and second gears simultaneously meshed in a meshed region; a first bearing insert located at a first end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the first bearing insert including an outlet channel fluidly coupling an outlet portion of the meshed region with the outlet port; and a second bearing insert located at a second end of the first and second pumping chambers and engaged with end surfaces of the first and second gears.
 18. A positive displacement gear pump comprising: a pump housing having an inlet port, an outlet port, and first and second pumping chambers; a first gear having helical teeth engaged with an inner surface of the first pumping chamber and a second gear with helical teeth engaged with an inner surface of the second pumping chamber, at least two teeth on the first and second gears simultaneously meshed in a meshed region; a first bearing insert located at a first end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the first bearing insert including an outlet channel fluidly coupling an outlet portion of the meshed region with the outlet port; and a second bearing insert located at a second end of the first and second pumping chambers and engaged with end surfaces of the first and second gears, the second bearing insert including a second inlet channel fluidly coupling an inlet portion of the meshed region with the inlet port. 